As device technology scales to smaller dimensions, leakage current may present problems if circuits are not properly designed. For example, leakage current may have an adverse effect on circuit robustness, which, in turn, may substantially diminish system reliability and performance.
Register files are particularly vulnerable to leakage current. Register files are basic building blocks in microprocessor systems, with modern designs having over 80. A source of leakage current in a register file system is DC offset, and particularly word-line DC offset as explained in greater detail below.
Conventional register files include a series of memory cells connected to a common word line. Up to 64 cells may be connected to the word line and all may be driven by the same word-line driver. In order to drive this number of cells with one driver, a long word line must be used. These word lines are typically 500 μm in length in a 0.13 μm technology node.
In this arrangement, the word-line driver is grounded by connecting an inverter within the driver circuit to some reference potential. Because of the length of the word line, the ground of far-end memory cells may be at a lower potential than the ground on the word-line driver. Such a potential difference (referred to as DC offset) will have the effect of increasing the leakage current exponentially on the associated bit lines. Since the bit lines are dynamic in nature, any increase in leakage current will necessarily affect the performance and reliability of the entire file in terms of its ability to accurately store data.